The invention relates to a method and a system for the controlled shutting-off of an internal-combustion engine which has a fuel injecting timing gear and an ignition control, and an electric machine in the form of one of a motor and a generator which is coupled directly or indirectly with the internal-combustion engine.
Conventionally, when an ignition key is turned into the "ignition-off" position, the injection and/or the ignition of an engine is switched off. This prevents a further combustion and the engine runs out corresponding to its moment of inertia.
However, in the case of such a shut-off operation, the problem arises that unburnt gasoline-air mixture still remains in the combustion space or the intake system. When the engine is started again, this effect results in poor emission values. With a view to future emissions laws, it is required to eliminate the unburnt gasoline-air fractions before the start of an engine.
This may take place in that the timing gear switches off the injection after the "ignition-off" signal but continues to trigger the ignition. However, because of the residual gas quantities which must then still be burnt, the engine will then run out in an undefined manner. This is called an "afterdieseling".
It is an object of the invention to ensure the removal of unburnt gas quantities in the engine while its running-out behavior is defined.
With respect to the method and to the system, this object is achieved by a system operable to carry out the following steps: detecting a shut-off signal for the internal-combustion engine, interrupting the fuel injection while simultaneously maintaining the ignition in response to the shut-off signal, maintaining a defined rotational engine speed for a defined time period or a defined number of crankshaft revolutions after the shut-off signal by means of the electric machine, and subsequently stopping the internal-combustion engine by means of the electric machine.
An important idea of the invention is the fact that, also after the ignition-off signal, the internal-combustion engine continues to be operated for a defined time period with a defined revolution and a switched-on ignition control. Since, according to the invention, the fuel injection is switched off in this time period, the unburnt gas quantities still situated in the intake system and the combustion space are burnt without residues. After the burning of the residual unburnt gas quantities, a rapid stopping of the internal-combustion engine is caused by acting upon the internal-combustion engine by means of the electric machine. A combined starter-generator arrangement, such as a crankshaft starter generator, is particularly suitable for use as the electric machine (starter, generator).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.